The invention relates to a drive device for a motor vehicle rear-view mirror in which at least one electric motor is provided in a housing consisting of an upper part and lower part, the output shaft of said motor meshing drivably with a spur gear mounted rotatably in a single bearing and tiltable within limits, said gear axially moving a nonrotatably mounted adjusting element by means of a threaded area, the free end of said element being coupled for articulation with the mirror support. The single bearing is a part-spherical snap-in seat formed in the lower part of the housing to receive a ball mounted integrally on the underside of the spur gear.
A drive device of this kind is known from Manzoni U.S. Pat. No. 4,598,605. In this known construction, during adjustment of the rear-view mirror, the adjusting element tilts relative to the spur gear, resulting in an increase in the adjusting force required for further rotational movement, and high wear on the threads. The required high retaining force of the single bearing produces an unsatisfactory effect under these conditions because it opposes the following movement of the spur gear into the tilted position of the adjusting element, so that the axes of the adjusting element and spur gear are only aligned in exceptional cases. A further increase in the adjusting force is produced by the large frictional radius (distance of the thread surfaces from the lengthwise axis). In addition, determination of the thread length is difficult in the known construction. Firstly, a degree of axial alignment which is as great as possible between the adjusting element and the spur gear must be produced, necessitating a long thread length, while on the other hand manual adjustment of the rearview mirror must be easy to perform, and this requires a short thread length because of the required provision for external engagement of the thread parts required for this purpose.
The goal of the invention is to provide an improved drive device of the type described so that it requires a lower adjusting force for the upward and downward movement of the adjusting element and ensures easy and always reliable manual adjustment of the rear-view mirror.